The present invention relates to novel stabilizers for chlorine-containing resins, and more particularly to stabilizers derived from pentaerythritol and/or polypentaerythritol for improving the heat stability of chlorine-containing resins.
It is well known that chlorine-containing resins, particularly polyvinyl chloride resins are unstable to heat and light and are colored or deteriorated by heat on processing. In order to minimize such coloration and deterioration due to heat and light, various stabilizers such as lead-, calcium-, zinc- and tin-stabilizers have been developed and used. However, in recent years environmental pollution by toxic heavy metals has become a social problem, and particularly the use of stabilizers having an excellent effect such as lead and cadmium stabilizers has been limited or regulated. Although the lead and cadmium stabilizers are being gradually replaced by nontoxic calcium-zinc, barium-zinc, and magnesium-zinc stabilizers, the effect of these nontoxic stabilizers is not so good as lead and cadmium stabilizers in substance. That is to say, the heat resisting effect of these nontoxic stabilizers is far inferior to that of the lead or cadmium stabilizers.
In order to provide stabilizers which have an excellent effect and are nontoxic, various attempts have been made, but no satisfactory stabilizer has been reported. It is known that polyols such as pentaerythritol, trimethylolpropane and neopentyl glycol have an effect as an auxiliary thermal stabilizer for chlorine-containing resins. However, these polyols have the disadvantages in their high water-solubility, sublimation and compatability at processing temperatures with resins. Although pentaerythritol and dipentaerythritol, tested in PL Standards, C-14-(10) of Japan Hygienic PVC Association, have a relatively low solubility in water and are known to be nontoxic, they have a high melting point and do not melt at a temperature of processing chlorine-containing resins. The compatibility with the resins is so poor that they are not dissolved in processed articles and decrease mechanical strength of articles.